The taxi fare won't be more than 4 USD. They also charge for the number of luggage you put in the back. I don;t know how much you are paying for Octave but Mookia is about less than 5 minutes walk from the Male ferry jetty.
You do not need a taxi to go to Mookai. Yes it is very safe in Male to take a taxi any time of the day or night. Night charges are slightly higher after midnight. Once you get out of the customs, just slightly to the left is the Information Counter for the airport. They should be able to help too if the hotel rep is not there. Many a times the hotels in Male do not have their airport reps at the airport. The bigger hotels in Male do so but the smaller ones do not.
vnfilm1, why do you need to stay just one night in Male? Where are you going after that? That may solve your stay in Male too? Depending on your final destination, if you are staying in a resort then they will help you at the airport. If you are going to an inhabited island, then it is a different story.